Assume the same fact pattern as set forth in the previous question (number 1), except that the agreement between Adam and Bob requires Bob to pay the $100 to Adam (not Cathy). Adam mows Bob's lawn, but Bob does not pay Adam anything. Cathy knows that Adam has mowed Bob's lawn, that Bob has not paid Adam, and that Adam cannot pay Cathy the $100 that Adam owes to Cathy until Adam receives the $100 from Bob. Can Cathy sue Bob to make Bob pay the $100 to Adam? Why or why not?